1. Field of the Invention
The present invention relates to mobile radio systems. To be more precise, it relates to a system for transmitting digital signals between two equipment units of a mobile radio network.
2. Description of the Prior Art
To respond to the multiplicity of new services, telecommunication networks such as ISDN (Integrated Services Digital Network) fixed telephone networks and GSM (Global System for Mobile communication) and PCS (Personal Communication System) mobile telephone networks convey digital signals in accordance with a digital transmission protocol. This is known in the art.
The digital links of such networks, for example pulse code modulation (PCM) links, transport each digital signal independently and in the form of packets containing both signaling information associated with the processing of a call and voice and/or data information.
Digital links of the above kind are used at an interface between two equipment units to enable interworking thereof, for example. One prior art example of this is the A interface which in GSM and PCS networks connects a mobile-services switching center (MSC) and a base station controller (BSC).
There are still many areas with no digital links, mainly because the latter necessitate specific and costly transmission infrastructures and sophisticated signal processing software.
The economic factor is therefore retarding in particular the expansion of networks such as GSM and PCS networks. For example, in the case of an A interface, installing a base station controller (BSC) and upgrading a conventional telephone exchange (e.g. a landline telephone exchange) for conformance with GSM and PCS networks are relatively low cost operations. On the other hand, installing the digital link supporting the digital protocol to the MSC is costly.
An object of the present invention is to provide a less costly and more flexible transmission system by adapting the predefined digital transmission protocol, to facilitate the deployment of mobile radio networks.